In many cardiovascular surgical procedures, and some nonsurgical therapeutic/supportive procedures, cardiopulmonary bypass systems are utilized to accomplish blood oxygenation and circulatory support while normal cardiopulmonary function of a patient is interrupted or impaired. Basically, the typical cardiopulmonary bypass systems of the prior art comprises (a) a venous reservoir for pooling and collecting venous return blood, (b) a pump for circulating the venous return blood and (c) an oxygenation device for oxygenating venous return blood prior to reinfusion of the blood into the vasculature of the patient. Additionally, cardiopulmonary bypass systems which are utilized during cardiothoracic surgical procedures typically incorporate an additional cardiotomy reservoir/filter component wherein blood suctioned from the operative site is collected, filtered and shunted into the above-mentioned venous reservoir wherein the filtered cardiotomy blood is combined with the venous return blood for subsequent pumping, oxygenation and return to the patient. Such cardiotomy reservoir/filter component is often fluidly attached to the venous blood accumulator or reservoir such that the venous blood accumulator or reservoir will receive and hold the filtered cardiotomy blood in combination or admixture with venous return blood received from the right heart or vena cava of the patient.
The venous blood accumulator or "venous reservoir" commonly consists of either a flexible bag or hard shell vessel having a blood inlet for receiving an inflow of blood, and a blood outlet for subsequent outflow of blood into the attendant portions of the bypass system (e.g. into the pump and/or membrane oxygenator). In surgical applications wherein the above-described cardiotomy reservoir component is employed, the blood inlet of the venous reservoir receives a mixture of (a) venous return blood obtained directly from the right atrium or vena cava of the patient, and (b) filtered cardiotomy blood which has been suctioned from the operative sight and preprocessed (e.g. filtered and defoamed) in the separate cardiotomy reservoir/filter.
The venous reservoir is desirably adapted to accommodate fluctuations in pooled blood volume brought about by relative variations in the rate of blood inflow (e.g. changes in venous return or cardiotomy blood volume) and/or the rate of blood outflow (e.g. changes in the rate of the bypass system pump). One means of accommodating such fluctuations in pooled blood volume is to provide a flexible bag-like venous reservoir which is capable of expanding and contracting in accordance with the normal variations in pooled blood volume with the reservoir.
Flexible bag-type venous reservoirs of the prior art are described in U.S. Pat. No. 4,493,705 (GORDON ET AL), U.S. Pat. No. 4,643,713 (VIITALA), U.S. Pat. No. 4,734,269 (CLARKE ET AL), U.S. Pat. No. 4,795,457 (COONEY) and U.S. Pat. No. 4,863,452 (IRMITER ET AL). Additionally, other types of venous return reservoirs (e.g. rigid, hard shell reservoirs) are described in U.S. Pat. No. 4,698,207 (BRINGHAM ET AL), U.S. Pat. No. 4,737,139 (ZUPKAS ET AL) and U.S. Pat. No. 4,756,705 (BEIJBOM ET AL).
The flexible bag-type venous reservoirs of the prior art have assumed various shapes and configurations and have incorporated various filters and vent tubes for removing bubbles or entrained air from the blood. For example, U.S. Pat. No. 4,493,705 describes a bag-type venous reservoir which is formed in an inverted "U" shape such that bubbles Within the blood may rise to the upper most point of the inverted "U" configuration, and be subsequently vented therefrom by way of an attendant vent port. Also, a filter screen is positioned near the midpoint of the "U" shaped bag to facilitate removal of air bubbles from the blood. Others of the flexible bag-type venous reservoirs have utilized various different shapes, configurations and filter elements to facilitate trapping and removal of entrained bubbles from return blood passing therethrough.
Because none of the venous reservoirs of the prior art have proven to provide consistently optimal bubble removal and/or optimal flow performance in all applications, there remains a need in the art for further improvements and refinements in the configuration, construction and function of such venous reservoirs.